The present invention relates to a rear converter for use in a camera having interchangeable lenses. More particularly, the invention relates to a rear converter which can be used between a camera body having an AF/(auto-focusing) capability and a conventional interchangeable photographing lens having no AF capability so as to enable the conventional photographing lens to be used for AF photographing.
Generally, a lens-interchangeable camera has an AE (automatic exposure) capability. For execution of such AE, data of lens characteristic values such as an open lens-stop value (full-opened diaphragm value) and a minimum lens-stop value (full-closed diaphragm value) for each photographing lens and data for change-over between automatic exposure control mode and manual exposure control mode must be transmitted to the camera body. Accordingly, data-transmission electrical contacts are provided both on the camera body and on the photographing lens so as to be connected in a predetermined relation.
An example of such data-transmission electrical contacts, as disclosed in Japanese Patent Unexamined Publication No. 162531/1984 filed by the present applicant, is shown in FIGS. 1 through 4.
The design of the aforementioned electrical contacts takes into account the fact that the AF body is designed to receive lenses having an AF capability as well as conventional photographing lenses which have no AF capability.
A photographing lens having an AF capability and capable of being mounted on the AF body is described in Japanese Patent Application Publication No. 234141/1986, also filed by the present applicant. This photographing lens is also designed to be usable with conventional camera bodies which have no AF capability, based on the same design philosophy as described above for the AF body.
For camera users who use only the AF body, it is, however, unnecessary for photographing lenses to be usable with other camera bodies. Such photographing lenses are provided as exclusive parts. By providing these photographing lenses as exclusive parts, the cost of the lenses can be reduced.
In FIGS. 1 to 4, reference numeral 211 designates a camera body, 213 a mount of the camera body, 215 a photographing lens, and 217 a mount of the photographing lens.
Each of the mounts 213 and 217 is also made of an electrically conductive material, for example, a material prepared by applying a plating treatment or the like to brass. Each of the mounts 213 and 217 serves as a connector between the camera body 211 and the photographing lens 215 and as an electrical ground.
The mount 213 of the camera body 211 is provided with an electrical contact group 227, for example, a group composed of five electrical contacts 221a, 222a, 223a, 224a and 225a electrically insulated from the mount 213 and arranged so as to be projectable from the surface of the mount 213.
The aforementioned electrical contacts are provided on the mount 213 and 217 in the manner to now be described.
FIG. 1 is a front view showing the camera body 101 seen from the mount. FIG. 2 is a rear view of a lens used with the camera body shown in FIG. 1. FIG. 3 is a schematic sectional view taken along a line I--I in FIG. 1 showing the electrical contact 221a. Similarly, FIG. 4 is a schematic sectional view taken along a line II--II in FIG. 1 showing the electrical contact 231a.
Each of the electrical contacts designated by reference numerals 221a, 223a, 224a, and 225a is electrically insulated from the mount 213 and is provided so as to be able to project from the surface of the mount. That is, as shown typically by the contact indicated by reference numeral 221a in FIG. 3, each of the electrical contacts is electrically insulated from the mount 213 by an insulating layer 18 and normally projects from the surface of the mount 213 (as shown by the solid line in FIG. 3). Further, each of the contacts is provided with a spring 19 which urges the contact against the mating contact when a photographing lens or rear converter is mounted to the camera body 211 (as shown by the broken line of FIG. 3).
The electrical contact designated by reference numeral 231a is electrically insulated from the mount 213 and provided so as to be unable to project from the surface of the mount (FIG. 4). The structure of the contacts 221a, 222a, 223a, 224a and 225a is as illustrated in FIG. 3.
The mount 217 of the photographing lens 215 is provided with an electrical contact group 229 corresponding to the electrical contact group 227. The electrical contact group 229 is composed of five electrical contacts 221b, 222b, 223b, 224b and 225b as shown in FIG. 2, which are not projectable from the surface of the mount 217 and which are electrically insulated from the mount 217. That is, the contacts 221b, 222b, 223b, 224b and 225b are constructed as illustrated in FIG. 4.
Further, the mount 213 of the camera body 211 is provided with another electrical contact 231a electrically insulated from the mount 213 and arranged so as to not project from the surface of the mount 213. That is, the structure is the same as that illustrated in FIG. 4. The mount 217 of the photographing lens 215 is also provided with an electrical contact 231b corresponding to the electrical contact 231a, the electrical contact 231b being electrically insulated from the mount 217 and arranged so as to be able to project from the surface of the mount 217 as shown in FIG. 3.
When the aforementioned photographing lens 215 is mounted on the aforementioned camera body 211, respective data are transmitted as follows. The data of the open lens-stop value is transmitted through three pairs of contacts (221a, 221b), (222a, 222b) and (223a, 223b) included in the electrical contact groups 227 and 229. The data of the minimum lens-stop value is transmitted through two pairs of contacts (224a, 224b) and (225a, 225b) included in the electrical contact groups 227 and 229. The data for change-over between automatic exposure control mode and manual exposure control mode is transmitted through the electrical contact 231a (as described in detail later). For example, the data of lens characteristic values are transmitted as follows.
The contacts included in the lens-side electrical contact group 229 are pretreated corresponding to the type of the photographing lens such that some contacts are coated with an insulating material while others are not and are free to make electrical connections with corresponding contacts on the body-side mount. A voltage is supplied through body-side pull-up resistors so that the voltage level at each of the insulated contacts is raised and the voltage level at each of the other contacts connected to the mount (grounded contacts) is reduced. Thus, the data of lens characteristic values is obtained by the combination of such high and low signals generated corresponding to the respective data of lens-stop values.
The data for change-over between automatic exposure control mode and manual exposure control mode may be generated as follows. The lens-side electrical contact 231b is connected to the lens-side mount 217 (i.e., the contact 213b is grounded). When a stop ring incorporated in the photographing lens is set in a predetermined position, the lens-side contact 231b touches the body-side contact 231a. When the stop ring is rotated from the predetermined position, the lens-side electrical contact 231b is moved away from the body-side electrical contact 231a. Thus, the data for change-over between automatic exposure control mode and manual exposure control mode is obtained on the basis of two states, namely, whether or not the lens-side electrical contact 231b touches the body-side electrical contact 231a.
These data are inputted to the controller in the camera body.
Although the aforedescribed data-transmission electrical contacts are simple in construction, the data for lens characteristic values and the data for change-over between the automatic exposure control mode and the manual exposure control mode can be securely transmitted to the camera body.
A further example of a lens-interchangeable camera having an AF capability is disclosed in Japanese Patent Unexamined Publication No. 4916/1985. FIG. 5 is a diagram showing such a camera having such an AF capability.
The camera of this type has a mechanism for automatically moving a lens of the photographing lens group to the focused position. More exactly, the photographing lens 241 for the AF camera has a plurality of lens elements including a lens 243 movable for focusing, a motive power transmitting device 245 for moving the movable lens 243, and a ROM (read-only memory) 247 for storing information (called "lens characteristic data") such as data indicative of open or minimum lens-stop values of the photographing lens 241, data indicative of photographic conditions corresponding to the position of the lens while being moved for focusing, and the like.
On the other hand, the camera body 251 of the AF camera includes a controller 253 for effecting AE and AF operations, an actuator 55 for moving the lens of the photographing lens group to the focused position, and other necessary parts.
In the prior art, photographing lenses of a type provided with an AF capability have been designed to be used together with an exclusive camera body 251. Accordingly, various kinds of data necessary for AE and AF control must be transmitted through exclusive data-transmission electrical contacts 261.
For the benefit of the camera user, it is desired that expensive camera bodies and photographing lenses be interchangeable so that they need not be replaced by new products whenever new bodies or lenses appear on the market. However, in the prior art photographing lens having an AF mechanism, a problem exists in that the photographing lens is not interchangeable with both a camera body having an AE capability and a camera body having an AF capability. provided in the same manner as those described above for the camera body and photographing lens.
In the following, a conventional rear converter installed between the aforementioned camera body 211 and photographing lens 215 will be described with reference to FIG. 6, which is a schematic block diagram showing the conventional rear converter.
In FIG. 6, reference numeral 311 designates a conventional rear converter. The rear converter has a body mount 313 for attachment to a mount of the camera body 211 as described above, a lens mount 315 for attachment to a mount of the photographing lens 215 as described above, and a fixed lens system 317 composed of a plurality of lenses for changing the focal length of the photographing lens 215. The body mount 313 of the rear converter 311 includes an electrical contact group 327 corresponding to the electrical contact group 227 of the camera body 211, and an electrical contact 331a corresponding to the electrical contact 231a of the camera body 211. The lens mount 315 of the rear converter 311 includes an electrical contact group 329 corresponding to the electrical contact group 229 of the photographing lens 215, and an electrical contact 331b corresponding to the electrical contact 231b of the photographing lens 215.
Each of the contacts 321a, 322a, 323a, 324a and 325a is incapable of projecting from the body mount 313 and is electrically insulated from the body mount 313. Each of the contacts 321b; 322b, 323b, 324b and 325b is capable of projecting from the lens mount 315 and is electrically insulated from the lens mount 315.
The electrical contacts 321a, 322a, 323a, 324a and 325a, as constituent members of the electrical contact group 327, are respectively electrically connected to the electrical contacts 321b, 222b, 323b, 324b and 325b, as constituent members of the electric contact group 329.
Accordingly, the change in the focal length of the photographing lens 15 and the transmission of data such as lens-stop data between the camera body 11 and photographing lens 15 can be attained.